The present invention relates to instrument systems for measuring rotational torque and is characterized by a rigid axial and radial support for the torque interconnect element.
State of the art torque interconnects such as coiled springs suffer high speed and rotational forces and weak radial alignment from significant errors introduced by wire stretching and frictional drag. Some examples of state of the art instruments are the DV-2, 3 viscometers of Brookfield Engineering Laboratories, Inc., Stoughton, Mass., U.S.A.
It is an object of the invention to overcome such difficulty.
It is a further object to provide a very high speed capability.
It is a further object of the invention to accomplish tight alignment.
It is a further object of the invention to minimize or eliminate rotational friction in a rigid support structure.
It is a further object of the invention to provide a means for dampening vibrations; such vibrations can prove detrimental to the torsional accuracy of such torsion systems.
The invention comprises measuring or responsive instruments, including (but not limited to) viscometers, having a music wire (20) or like high tensile wire support between driving/driven shaft assemblies (18, 16) and appropriate mounting to eliminate drag, friction, radial misalignment, vibration problems, especially at high rotational speeds, and afford an enhanced accuracy and speed of measurement or other response of the instrument as a whole, including such specific features allowing large angular deflections or small ones (full scale under one degree) and axial and radial rigidity. The instrument can also be used with a plate for oscillation and normal force measurements.
The invention provides a wire torsion mount of high tensile strength, e.g. music wire, a hardened steel wire with a tensile strength of 90,000 psi with an elastic modulus (E) of 27.6xc3x97106 psi and shearing modulus (G) in torsion of 10.6xc3x97106 psi. However, the invention is applicable broadly to wires with E and G values sufficiently high to provide axial support while allowing significant elastic deformation in torsional rotation. The wire avoids permanent axial deformation even when supporting axial loads of 10 pounds or more (typically 2-4 pounds in the following context of the next paragraph, but other loads in other contexts).
In the viscometer context, wires of 0.003-0.025 inch diameter wires are used, typically 0.006 inch or 0.012. Such a wire is mounted at the center of rotation of a rotational drive system of a viscometer and because of its small diameter and relatively long length (typically two inches in relation to a 0.012xe2x80x3 diameter wire and generally over 100:1 length to diameter), has low rotational torque and essentially no centrifugal force even when rotated at high speeds. A range of torque of 0 to 10,000 dyne-cm (typically, about 7,000) is realized over a full scale angular deflection range of 45 to 90xc2x0 (typically about 75xc2x0). The wire is surrounded near or at each end by a jewel bearing for radial support, thereby assuring accurate concentric alignment of the rotational drive system. Radial deflection tendencies of the torsion assembly are substantially counter-acted by the bearing.
The foregoing length to diameter considerations can be modified in certain situations, e.g. the multiple wire arrangements of certain embodiments described below. Small deflection angles can be generated using shorter lengths and/or lower length to diameter ratios (i.e. over 50:1). The smaller angle allows a lower stiffness and/or a higher sensitivity at a given stiffness or a combination of these factors.
Preferrably, the wire torsional modulus and wire diameter are such as to provide a torsional resistance over an angle of less than 2xc2x0 under 10,000 dyne cm.
Other objects, features and advantages will be apparent from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings in which: